I too am having the same problem.
I started to have it after importing all of the 3.0.4 spring-samples.
I had https://src.springframework.org/svn/spring-samples checked out to folder on my hdd and imported them as existing projects.
STS won't close and a project, that was ok before, has errors in it.
OS: win xp sp3
console maven output
last line in my console:
1.05.11 0:28:00 EEST: Downloaded http://repository.springsource.com/maven/bundles/release/org/apache/tiles/tiles-api/2.2.0/tiles-api-2.2.0.pom